(a) Field of the Invention:
The present invention relates to a flare stop and, more particularly, to a flare stop to be used with a large aperture ratio zoom lens system in order to shut off offaxial rays which cause flare.
(b) Description of the Prior Art:
Known zoom lens systems in which a stop, which is arranged that the diameter thereof is varied in co-operation with the movement of lens groups for the purpose of zooming, is provided in addition to an aperture stop are disclosed, for example, in Japanese published examined patent application No. 20147/65 and Japanese published unexamined patent application No. 122348/74.
Out of them, the known zoom lens system disclosed in Japanese published examined patent application No. 20147/65 is arranged that a movable lens which retracts is provided with a flare stop, which is arranged that the diameter thereof is varied in co-operation with the movement of said movable lens, in order to prevent flare which is caused by rays reflected by the inner surface of the lens mount and which increases according to the retracting movement of said movable lens.
Said flare stop in said known zoom lens system resembles the flare stop according to the present invention from the view point that the diameter thereof is varied in co-operation with the movement of the movable lens. However, the object of said known flare stop is different from the object of the flare stop according to the present invention arranged to eliminate coma flare which occurs in the portion of intermediate image height when a zoom lens system with a constant F number is put to the state of wide position as described later in detail.
The flare stop disclosed in Japanese published unexamined patent application No. 122348/74 is provided to a zoom lens system, which comprises a movable subsystem and a fixed subsystem, in order to shut off the unnecessary offaxial rays when arranging the lens system as a double zooming system so as to make the field angle wider by further providing a movable lens group in the fixed subsystem, which has a stop at the front part thereof. Therefore, the object, functions, etc. of said flare stop are also different from those of the flare stop according to the present invention.